Systems and methods of optical coherence tomography with a multi-focal delay line

ABSTRACT

An optical coherence tomography (OCT) system includes: a light source; a multi-focal delay line; and a light detector. The multi-focal delay line includes: a positive lens; and an optical switch configured to: receive a light from the light source; selectively direct the sample light to the positive lens via a selected one of a plurality of light interfaces each located a different distance from the focal plane of the positive lens; and direct the sample light to an object to be measured. The light detector is configured to receive return light returned from the object to be measured in response to the sample light, and to receive a reference light produced from the light from the light source, and in response thereto to detect at least one interference signal. An associated OCT method may be performed with the OCT system.

RELATED APPLICATIONS

This application is a non-provisional application and claims the benefitunder 35 U.S.C. § 119(e) of U.S. Provisional Application Ser. No.62/113,196, filed Feb. 6, 2015, which is incorporated herein in itsentirety by reference.

BACKGROUND Field

This invention generally pertains to the field of vision diagnostics,and in particular, to a method and system for objectively measuring anoptical characteristic of an eye.

Description

Optical coherence tomography (OCT) is an established imaging techniquethat uses light to capture micrometer-resolution, three-dimensionalimages from within optical scattering media, including for example,biological tissue. OCT is based on low-coherence interferometry thattypically employs near-infrared light. Using relatively long wavelengthlight allows the light to penetrate into the scattering medium.Depending on the properties of the light source, OCT can achievesub-micrometer resolution (with very wide-spectrum sources emitting overa ˜100 nm wavelength range).

OCT has applications in ophthalmology, where it can be used to obtaindetailed images of different features of the eye.

OCT may be employed in an optical measurement instrument, which performscataract diagnostics or pre-operational cataract treatment planning thatmay include specification and/or selection of an appropriate intraocularlens (IOL) for a particular patient, and/or post-surgical test andevaluation after an IOL has been implanted, etc.

Typically, to measure the entire eye, existing OCT instruments adjustthe collimation/focusing in the sample arm of the interferometer toobtain optimum return signals from the different elements or regions ofthe eye. For example, the best corneal return signals are obtained whenthe sample light is focused on the cornea, while the best retinal returnsignals are obtained when the sample light is focused on the retina.Additionally, the time delay between the sample optical path and thereference optical path must be adjusted for the different regions of theeye for OCT instruments having a depth range of less than 50 mm in air.Additionally, in an eye measurement instrument where the eye is notphysically constrained, the measurements of all regions and elements ofthe eye should be measured within a very short time of each other (e.g.,within a total time period of 80 msec.) so as to avoid the possibilityof eye movement that may diminish or degrade the quality or accuracy ofthe measurements.

Currently, OCT instruments typically either adjust the collimation/focusby means of a lens that is translated along the optical axis of theinstrument (e.g., using a linear motor or voice coil type actuator), orchange the focal length of a lens through electro-optic or “liquid lens”technology. Of the translation devices, linear motor translators areslow, requiring fractions of a second, and therefore, are highlysusceptible to eye movement during the measurements. The voice coil typeactuators can translate the lens in a time frame on the order of 10msec, but they are generally expensive. Electro-optic lenses can beadjusted sufficiently rapidly, but they are expensive and not alwayscompatible with the wide optical bandwidth required for an OCTinstrument. Liquid lenses can be quite economical, but are generally notthermally stable, can introduce aberrations that affect the returnsignal from the eye and typically can not be built to have effectiveanti-reflection coatings on the liquid interfaces.

Therefore, it would be desirable to provide a system and method foroptical coherence tomography (OCT) which can support relatively rapidOCT measurements in a cost effective manner. In particular, it would bedesirable to provide a cost effective system and method for opticalcoherence tomography (OCT) which can support measurements of an entirehuman eye within a timeframe which minimizes difficulties associatedwith a subject's movement of the eye during a measurement interval.

SUMMARY OF THE INVENTION

Hence, to obviate one or more problems due to limitations ordisadvantages in the related art, this disclosure provides embodimentsincluding a system comprising: a light source configured to emit light;a first optical system configured to receive the light from the lightsource and to produce therefrom reference light and sample light; areference optical path configured to receive the reference light fromthe first optical element; a multi-focal delay line, comprising: anoptical switch configured to receive the sample light from the firstoptical system and to selectively couple the sample light to a selectedlight interface among a plurality of light interfaces, and a positivelens system, wherein the light interfaces are all separated and spacedapart from the positive lens system and located at different distancesthan each other from an effective focal plane of the positive lens,wherein the positive lens system is configured to receive the samplelight from the selected light interface, to provide the sample light toan eye, to receive return light from the eye, and to provide the returnlight to the selected light interface, wherein the optical switch isfurther configured to provide the return light to the first opticalsystem; a light detector configured to receive the reference light fromthe reference optical path, and to receive the return light from thefirst optical system, and in response thereto to detect at least oneinterference signal; and one or more processors configured to controlthe optical switch to selectively couple the sample light to each of theplurality of light interfaces, one at a time, and further configured tomeasure at least one characteristic of the eye from the detectedinterference signal when the sample light is selectively coupled to theplurality of light interfaces. The signal may be a spatial distributionof light and dark fringes on a detector array for a spectral domain OCTsystem. Or, the signal may be a time varying voltage from balancedphotodectors for a swept source OCT system.

In some embodiments, the optical switch has a plurality of output ports,and the multi-focal delay line includes a plurality of opticalwaveguides each connected to one of the output ports, the plurality ofoptical waveguides providing the plurality of light interfaces.

In some versions of these embodiments, each of the light interfacescomprises a second end of a corresponding one of the optical waveguides.

In some versions of these embodiments, the system further comprises anintegrated optical circuit including the optical switch, an adjustableoptical delay, and the optical waveguides.

In some embodiments, the optical switch has a plurality of output ports,and wherein the multi-focal delay line comprises a plurality of opticalfibers each having a first end coupled to one of the plurality of outputports, and wherein each of the light interfaces comprises a second endof a corresponding one of the optical fibers.

In some versions of these embodiments, each of the optical fibers has adifferent length.

In some embodiments, the one or more processors are further configuredto determine at least one distance between two different components ofthe eye from the detected interference signal when the sample light isselectively coupled to the light interfaces.

In some versions of these embodiments, the distances include at leastone of: a distance between a reference plane and the anterior surface ofa cornea, a distance between a surface of a cornea and a surface of alens, a distance between a surface of the lens and a retina; and adistance between a surface of the cornea and the retina.

In some embodiments, the optical system includes at least one scanningdevice configured to scan the sample light on the eye in at least onedirection.

In some embodiments, at least one of the light interfaces is distancedfrom the positive lens so that the sample light provided from theoptical system to the eye is substantially focused on the retina.

In some versions of these embodiments, at least another one of the lightinterfaces is distanced from the positive lens so that the sample lightprovided from the optical system to the eye is substantially focused ona cornea of the eye.

In some versions of these embodiments, at least another one of the lightinterfaces is distanced from the positive lens so that the sample lightprovided from the optical system to the eye is substantially focused ona lens of the eye.

In some embodiments, the light produced by the light source has acoherence length, and wherein the light interfaces are arranged withrespect to the focal plane of the positive lens system such that thereturn light from the eye for a first one of the light interfacesprincipally comes from a first depth in the eye and the return lightfrom the eye for a second one of the light interfaces principally comesfrom a second depth in the eye different from the first depth, andwherein a distance between the first depth and the second depth isgreater than the coherence length.

In some versions of these embodiments, the system is further configuredto automatically change a delay provided by the multi-focal delay lineto match each of the first and second depths when the light is outputfrom the first one of the light interfaces and the second one of thelight interfaces, respectively.

In some embodiments, the light interfaces are all disposed within threedegrees of an optical axis of the positive lens.

In some embodiments, the first optical system includes a beam splitterconfigured to receive the light from the light source and to producetherefrom the reference light and the sample light.

In some embodiments, the first optical system includes a fiber opticalcoupler configured to receive the light from the light source and toproduce therefrom the reference light and the sample light.

In another aspect of the invention, a method comprises: producing samplelight and reference light from a common light source; controlling anoptical switch to direct the sample light to an eye via a first selectedlight interface and a positive lens; detecting at least one firstinterference signal from the reference light and return light returnedfrom the eye in response to the sample light being directed to the eyevia the first selected light interface; controlling the optical switchto direct the sample light to the eye via a second selected lightinterface and the positive lens, wherein the second selected lightinterface is disposed at a different distance from a focal plane of thepositive lens than the first selected light interface; detecting atleast one second interference signal from the reference light and returnlight returned from the eye in response to the sample light beingdirected to the eye via the second selected light interface; anddetermining at least one distance between at least two differentfeatures of the eye from the detected first and second interferencesignal.

In some embodiments, the first selected light interface is distancedfrom the positive lens so that the sample light provided to the eye issubstantially collimated.

In some versions of these embodiments, the second selected lightinterface is distanced from the positive lens so that the sample lightis focused on a cornea of the eye.

In some versions of these embodiments, the method further includesdetermining a distance between the cornea and a retina of the eye fromthe detected first and second interference signal.

In some versions of these embodiments, the method further includesscanning the sample light in at least one direction so as to create aplurality of first interference signals from the reference light andreturn light returned from the eye in response to the sample light beingdirected to the eye via the first selected light interface and to createa plurality of second interference signals from the reference light andreturn light returned from the eye in response to the sample light beingdirected to the eye via the second selected light interface.

In yet another aspect of the invention, a system comprises: a lightsource; a multi-focal delay line, comprising: a positive lens having afocal plane, and an optical switch configured to receive a light fromthe light source and to selectively direct the sample light to thepositive lens via a selected one of a plurality of light interfaces eachlocated a different distance from the focal plane of the positive lens,wherein the positive lens is further configured to direct the samplelight to an object to be measured; and a light detector configured toreceive the return light returned from the object to be measured inresponse to the sample light being directed to the object to be measuredvia the positive lens, and to receive a reference light produced fromthe light from the light source, and in response thereto to detect atleast one interference signal.

In some embodiments, the system further includes a controller configuredto: control the optical switch to direct the sample light to thepositive lens via a first one of the plurality of light interfaces tocreate at least one first interference signal from the reference lightand return light returned from the object to be measured in response tothe sample light being directed to the object to be measured via thefirst light interface; control the optical switch to direct the samplelight to the positive lens via a second one of the plurality of lightinterfaces to create at least one second interference signal from thereference light and return light returned from the object to be measuredin response to the sample light being directed to the object to bemeasured via the second light interface; and determine at least onedistance between at least two different features of the object to bemeasured from the first and second interference signal.

In some embodiments, the multi-focal delay line further comprises: aplurality of optical couplers, each optical coupler including: a firstport coupled to an output of the optical switch, a second port coupledto a corresponding return light input of the light detector, a thirdport coupled to a corresponding one of the plurality of lightinterfaces, and a fourth port; and a plurality of reference opticalpaths each coupled between the fourth port of a corresponding one of theplurality of optical couplers and a corresponding reference light inputof the light detector.

In some embodiments, the multi-focal delay line further comprises: aplurality of optical couplers, each optical coupler including: a firstport coupled to an output of the optical switch, a second port coupledto a first light input of the light detector, a third port coupled to acorresponding one of the plurality of light interfaces, and a fourthport; and a plurality of reference optical paths each coupled betweenthe fourth port of a corresponding one of the plurality of opticalcouplers and a second light input of the light detector.

In some versions of these embodiments, the system further comprises: afirst optical combiner having a plurality of inputs each of which iscoupled to the second port of a corresponding one of the plurality ofoptical couplers, and having an output coupled to the first light inputof the light detector; and a second optical combiner having a pluralityof inputs each of which is coupled to on output of a corresponding oneof the plurality of reference optical paths, and having an outputcoupled to the second light input of the light detector.

In some versions of these embodiments, the system further comprises: asecond optical switch having a plurality of inputs each of which iscoupled to the second port of a corresponding one of the plurality ofoptical couplers, and having an output coupled to the first light inputof the light detector; and a third optical switch having a plurality ofinputs each of which is coupled to on output of a corresponding one ofthe plurality of reference optical paths, and having an output coupledto the second light input of the light detector.

This summary and the following detailed description are merelyexemplary, illustrative, and explanatory, and are not intended to limit,but to provide further explanation of the invention as claimed.Additional features and advantages of the invention will be set forth inthe descriptions that follow, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription, claims and the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the invention are set forth with particularity inthe appended claims. A better understanding of the features andadvantages of the present invention will be obtained by referring to thefollowing detailed description that sets forth illustrative embodimentsusing principles of the invention, as well as to the accompanyingdrawings of which:

FIG. 1 is a functional block diagram of one embodiment of an opticalmeasurement system.

FIGS. 2A and 2B combine to form a more detailed diagram of portions ofone embodiment of an optical measurement system.

FIG. 3 is a functional block diagram of one embodiment of an opticalcoherence tomography (OCT) subsystem which may be included in an opticalmeasurement system.

FIGS. 4A and 4B illustrate one embodiment of a multi-focal delay line(MFDL) that may be included in an optical coherence tomographer.

FIG. 5 illustrates operation of an optical coherence tomography (OCT)subsystem which includes an MFDL.

FIG. 6 is a functional block diagram of another embodiment of an opticalcoherence tomography (OCT) subsystem which may be included in an opticalmeasurement system.

FIG. 7 is a functional block diagram of yet another embodiment of anoptical coherence tomography (OCT) subsystem which may be included in anoptical measurement system.

FIG. 8 is a functional block diagram of still another embodiment of anoptical coherence tomography (OCT) subsystem which may be included in anoptical measurement system.

FIG. 9 is a functional block diagram of a further embodiment of anoptical coherence tomography (OCT) subsystem which may be included in anoptical measurement system.

FIG. 10 is a functional block diagram of still a further embodiment ofan optical coherence tomography (OCT) subsystem which may be included inan optical measurement system.

FIG. 11 is a flowchart of an example embodiment of a method of measuringan optical characteristic of an eye.

DETAILED DESCRIPTION

The following description describes various embodiments of the presentinvention. For purposes of explanation, specific configurations anddetails are set forth so as to provide a thorough understanding of theembodiments. It will also, however, be apparent to one skilled in theart that embodiments of the present invention can be practiced withoutcertain specific details. Further, to avoid obscuring the embodimentbeing described, various well-known features may be omitted orsimplified in the description.

It would be desirable to incorporate an OCT system into an eyeinstrument for cataract diagnostics that also measures the refractivestate of an eye. Such a system may use a method of operation that candraw the eye into its farthest possible refractive state whenmeasurements are made, while also maintaining a large pupil size forboth younger subjects and older subjects.

As used herein, the term “light source” means a source ofelectromagnetic radiation, particularly a source in or near the visibleband of the electromagnetic spectrum, for example, in the infrared, nearinfrared, or ultraviolet bands of the electromagnetic radiation. As usedherein, the term “light” may be extended to mean electromagneticradiation in or near the visible band of the electromagnetic spectrum,for example, in the infrared, near infrared, or ultraviolet bands of theelectromagnetic radiation.

FIG. 1 is a functional block diagram of one embodiment of an opticalmeasurement instrument or optical measurement system 100 for measuringone or more characteristics of an eye 10. Optical measurement system 100includes a patient interface (e.g., a headrest and eye examinationarea), a camera 120, a corneal topographer 130, a wavefront aberrometer140, one or more displays 150, one or more processors 160 and associatedstorage (e.g., memory) 170, one or more operator input devices 180 forreceiving input or instructions from an operator 20, and an opticalcoherence tomography (OCT) subsystem 190. It should be understood thatoptical measurement system 100 is simply one embodiment for illustratingprinciples of the invention, and that many variations are possible whichmay omit certain elements, add additional elements, and/or change someof the elements. Some implementations may include additional elementsnot specifically shown in FIG. 1.

In some implementations, camera 120 may be an eye alignment camera whichis used to insure proper eye alignment when making corneal topography,wavefront aberrometry measurements, and/or optical coherence tomographymeasurements with corneal topographer 130, wavefront aberrometer 140,and/or OCT subsystem 190. Beneficially, camera 120 alone or inconjunction with processor(s) 160 may provide a continuous live displayof eye 10 to operator 20 via display 150.

Wavefront aberrometer 140 may measure wavefront aberrations of eye 10from which one or more optical characteristics may be ascertained. Asdescribed in greater detail below with respect to FIGS. 2A-B, wavefrontaberrometer 140 includes a fixation target for the subject to view whenmeasurements are made of eye 10.

Although example configurations of corneal topographer 130 and wavefrontaberrometer 140 will be described in further detail below with respectto FIG. 2A-B, it should be understood that these elements may employ anyof a variety of other configurations.

Display(s) 150 may include one or more display devices which provideimages and/or data to operator 20 under control of processor(s) 160.Such images and data may include operating instructions and/or requestsfor input from operator 20, images of eye 20 produced by camera 120,images and data reflecting measurements of eye 10 performed by cornealtopographer 130, wavefront aberrometer 140, OCT subsystem 190, etc.Display(s) 150 may include one or more flat panel displays, includingone or more touchscreens, individual lights (e.g., light emittingdiodes), or any other convenient display device(s).

Processor(s) 160 execute(s) computer-readable instructions forperforming operations of optical measurement system 100. Such operationsmay include: adjusting one or more operating parameters of cornealtopographer 130, wavefront aberrometer 140, and/or OCT subsystem 190;processing data output by corneal topographer 130, wavefront aberrometer140, and/or OCT subsystem 190 interpreting and responding to inputsand/or instructions received by operator input device(s) 180; generatingimages and/or data for display by display(s) 150; etc. In particular, asdescribed in greater detail below, processor(s) 160 may control oradjust a brightness level of a fixation target employed by opticalmeasurement system 100, for example as part of wavefront aberrometer140. Processor(s) 160 may perform into operations using instructionsand/or data stored in associated storage 170. Storage 170 may includeany combination of volatile memory devices (e.g., random access memory),nonvolatile memory devices (e.g., read only memory, FLASH memory),computer readable media such as hard disk drives, optical disks, etc. Inparticular, storage 170 may store an operating system for processor(s)160 and one or more computer programs which are executed by processor(s)160 during operation of optical measurement system 100. In someimplementations, storage 170 may store computer-readable instructionswhich cause processor(s) 160 to execute one or more algorithms formaking wavefront measurements of a subject's eye 10. In someimplementations, storage 170 may store computer-readable instructionswhich cause processor(s) 160 to execute one or more algorithms describedbelow, for example with respect to FIG. 11. In some implementations,storage 170 may store raw data produced by corneal topographer 130,wavefront aberrometer 140, and/or OCT subsystem 190, and/or data fromcorneal topographer 130, wavefront aberrometer 140, and/or OCT subsystem190 which has been processed by processor(s) 160.

Operator input device(s) 180 may include any combination of thefollowing devices: keyboard, touchscreen, touchpad, joystick,pushbuttons, roller ball, mouse, keypad, microphone, etc.

In general, processor(s) 160 operate in conjunction with display(s) 150and operator input device(s) 180 to provide a user interface forreceiving instructions and data from operator 20 and for communicatingwarnings, instructions, and data to operator 20. These warnings mayindicate to the operator when the quality of the signal data isdeficient in some manner and that the data should re-collected. Forexample, the fringe visibility (ratio of dark to light in the signal)might be low so the data should be re-collected. In another case, thefringe visibility itself may be good, but other conditions may existthat indicate the data should not be relied upon. For instance, thecorneal topography data may indicate poor tear film was present duringthe measurement, so the data should be recollected. In another example,the gaze of the patient may have wandered so the data should berecollected. In a combined instrument including corneal topography, irisimaging, wavefront sensor, and OCT, there are a number of combinationsof comparisons and correlations that may be performed to indicate if adata set is good. Whether such relationships are good may be summarizedby a data quality indicator. One use of such an indicator would be toguide an instrument operator regarding the measurement should be redone.Another use would be to provider an indicator to the doctor reviewingthe data later to help him or her understand if the data is reliable foruse.

FIGS. 2A and 2B combine to form a more detailed diagram of portions ofone embodiment of an optical measurement system 200. Optical measurementsystem 200 may be one embodiment of optical measurement instrument 100according to the block diagram of FIG. 1. In particular, FIG. 2A showselements of an optical coherence tomographer subsystem, such as opticalcoherence tomographer subsystem 190 of FIG. 1, and elements of a cornealtopographer subsystem, such as corneal topographer subsystem 130 ofFIG. 1. FIG. 2B shows elements of a wavefront aberrometer subsystem,such as wavefront aberrometer 140 of FIG. 7, and a fixation target.

In particular, FIG. 2A shows an optical coherence tomography (OCT)subsystem 290 and scanning mirrors 660. As discussed in greater detailbelow, OCT subsystem 290 can be controlled (e.g., by processor(s) 160)to selectively focus the OCT measurements at different parts of asubject's eye (e.g., anterior corneal surface; posterior cornealsurface; anterior lens surface; posterior lens surface; retinal surface;etc.).

FIG. 2A also shows a corneal topographer subsystem with an inner ringlight source and Helmholtz sources formed by an LED 1, a diffuser lensL8, and a plate 234 with holes for passing the diffused lighttherethrough. FIG. 2A also shows an iris camera 236. FIG. 2A showsvarious other optical elements such as: beam splitters BS1, BS2, BS4;lenses L1, L8 and L9; a quarter-wave plate QWP; mirrors M2 and M3; alaser and an LED1

FIG. 2B shows a wavefront aberrometer subsystem, including a wavefrontsensor 248 and an adjustable telescope 244 with a dynamic range limitingaperture 233 disposed between the lenses L3 and L4 of adjustabletelescope 244. Beneficially, wavefront sensor 248 and one of thetelescope lenses (e.g., L4) may be mounted on a movable stage 246 whichcan be adjusted to correct, for example, for up to 12 Diopters in themyopic range and up to 8 Diopters in the hyperopic range. FIG. 2B alsoshows a superluminescent diode (SLD) as a light source 242 for thewavefront aberrometer, and a fixation target in the visible light range,for example a video target 247.

In some embodiments, various subsystems of optical measurementinstrument 200 may operate with light at different wavelengths. Forexample, in some embodiments: the optical coherence topographersubsystem may operate with light at a wavelength of about 1060 nm; theHelmholtz sources of the corneal topographer subsystem may operate at awavelength of about 760 nm; the iris camera may use light at both 760 nmof the Helmholtz sources and at 950 nm; fixation target 247 may operatein a visible wavelength range of 500-600 nm; and wavefront sensor 248may operate at a wavelength of about 840 nm.

Beneficially, wavefront sensor 248 may be Shack-Hartmann wavefrontsensor comprising a detector array and a plurality of lenslets forfocusing received light onto its detector array. In that case, thedetector array may be a CCD, a CMOS array, or another electronicphotosensitive device. Embodiments of wavefront sensors which may beemployed in one or more systems described herein are described in U.S.Pat. No. 6,550,917, issued to Neal et al. on Apr. 22, 2003, and U.S.Pat. No. 5,777,719, issued to Williams et al. on Jul. 7, 1998, both ofwhich patents are hereby incorporated herein by reference in theirentirety. However, other wavefront sensors may be employed instead.

Wavefront sensor 248 outputs signals to processor(s) 160 which use(s)the signals to determine ocular aberrations of eye 10. Beneficially,processor(s) 160 is/are able to better characterize eye 10 byconsidering the corneal topography of eye 10, which may also bedetermined by processor(s) 160 based on outputs of detector array 1400,as explained above.

FIG. 3 is a functional block diagram of one embodiment of an opticalcoherence tomography (OCT) subsystem 300 which may be one embodiment ofOCT subsystem 190 included in optical measurement system 100 and/or 200.

OCT subsystem 300 includes a light source 310, an optical device 320, amulti-focal delay line (MFDL) 325, and a light detector 350.

In some embodiments, light source 310 may comprise a superluminescentdiode (SLD). In some embodiments, light source 310 may be a swept lightsource. In some embodiments, light source 310 may emit light at a centerfrequency at or near 1060 nm.

As illustrated in FIG. 3, optical device 320 is a four port device, withports A, B, C and D labeled in FIG. 3. In some embodiments, opticaldevice 320 may be a beam combining element, here also referred to as an“optical coupler”—for example a plate beam splitter, a beam splittingcube, or fiber optic coupler.

Multi-focal delay line 325 includes an optical switch 330 and a positivelens 370.

In some embodiments, optical switch 330 may comprise a fiber opticswitch. In some embodiments, optical switch 330 may comprise amicroelectromechanical systems (MEMS) switch. In some embodiments,optical switch 330 may comprise an electro-optical switch. In someembodiments, optical switch 330 may be realized via a photonicintegrated circuit (PIC) or integrated optical circuit.

FIGS. 4A and 4B illustrate one embodiment of a multi-focal delay line(MFDL) 400 which may be included in an optical coherence tomographer,such as OCT subsystem 300 of FIG. 3. That is, MFDL 400 may be oneembodiment of MFDL 325 of FIG. 3.

As shown in FIG. 4A, MFDL 400 includes optical switch 330 and positivelens 370. Optical switch 330 has an input 432 and a plurality of outputs434 each coupled to a first end of a corresponding optical fiber 441,442, 443 and 444. For reasons that will be explained below, each of theoptical fibers 441, 442, 443 and 444 may have a corresponding differentlength, which can be obtained, for example, by loops of fiber 451, 452and 454.

As illustrated in FIG. 4B, each of the optical fibers 441, 442, 443 and444 has a corresponding second end which forms a light interface 461,462, 463 and 464, respectively. Each of the light interfaces 461, 462,463 and 464 is located a corresponding different distance from a backfocal plane 4000 of positive lens 370 and is oriented parallel to anoptical axis 4100 of positive lens 370. Beneficially, light interfaces461, 462, 463 and 464 are all arranged near optical axis 4100. In someembodiments, light interfaces 461, 462, 463 and 464 are all arrangedwithin about 3 degrees of optical axis 4100.

Further details of embodiments of light detector 350 will be providedbelow.

An example operation of an optical coherence tomographer OCT subsystem300 will now be described with respect to FIG. 5, wherein it is assumedthat MFDL 325 is embodied by MFDL 400 of FIGS. 4A-B. In the descriptionto follow, it will be assumed that optical device 320 is an opticalcoupler, for example a fiber optic coupler. However it will beunderstood that in other embodiments optical device 320 may have adifferent structure or configuration while still providing thefunctionality as described below.

Turning back to FIG. 3, light 301 from light source 310 is provided tofirst port “A” of optical coupler 320. In response to light 301 receivedfrom light source 310, optical coupler 320 outputs sample light at port“C” to a sample optical path 303 and outputs reference light at port “D”to a reference optical path 304.

Light detector 310 has a pair of inputs, labeled “X” and “Y” in FIG. 3,and the reference light output from port “D” of optical coupler 320 isprovided to the input “Y” of light detector 350 via reference opticalpath 304. In some embodiments, reference optical path 304 from port “D”of optical coupler 320 to the input “Y” of light detector 350 mayinclude a variable optical attenuator (VOA) and/or a delay element whichare not shown in FIG. 3 to simplify the illustration. In someembodiments, the delay element may be a variable delay element, forexample a variable air-gap delay.

Meanwhile, the sample light 303 output at port “C” of optical coupler320 is provided to input 432 of optical switch 330. Optical switch 330is controlled via one or more control inputs 433 to selectively providethe light received at input 432 to one of the light interfaces 461, 462,463 and 464 via a selected optical fiber among optical fibers 441, 442,443 and 444.

The sample light is provided from the selected one of the lightinterfaces 461, 462, 463 and 464 to positive lens 370, which may be partof a positive lens system including other optical components such asother filters, lenses, etc. not shown in FIGS. 3 and 4A-B.

Positive lens 370 directs sample light 345 to eye 10, for examplethrough an optical system not shown in FIG. 3, which may include thepair of scanning mirrors 660 for scanning the sample light 345 in twoorthogonal directions on eye 10.

As noted above, each of the light interfaces 461, 462, 463 and 464 isdisposed or located at a different distance from back focal plane 4000of positive lens 370. By selecting a particular light interface 461,462, 463 or 464 in response to a control signal received (for examplefrom processor(s) 160) at control input 433, optical switch 330 providessample light 345 to positive lens 370 to be directed to measure adifferent region of eye 10.

FIG. 5 illustrates different features or regions of eye 10 which may bemeasured or characterized by OCT subsystem 300. In particular, FIG. 5shows a first region 5101, a second region 5102, a third region 5103,and a fourth region 5104 of eye 10. First region 5101 generallycorresponds to a region including retina 16 of eye 10; second region5102 generally corresponds to a region including a posterior surface oflens 14 of eye 10; third region 5103 generally corresponds to a regionincluding an anterior surface of lens 14 of eye 10, and fourth region5104 generally corresponds to a region including cornea 12 of eye 10.

Although FIG. 5 shows four regions, in general eye 10 may be dividedinto any convenient number of regions to be measured or characterized byan MFDL having a corresponding number of light interfaces. In someembodiments, the regions may span the entire depth of eye 10.Beneficially, the depth of each region may be matched to the coherencelength of sample light 354 produced by light source 310. That is, thedepth of each region may be less than the coherence length of samplelight 354. For example, in some embodiments, each region has a depth of4-7 mm.

In operation, MFDL 400 allows OCT subsystem 300 to selectively measureor characterize any of the regions 5101, 5102, 5103 and 5104 of eye 10by directing sample light 345 to corresponding focus positions 5001,5002, 5003 and 5004.

For example, in FIG. 4B it is seen that light interface 461 is locatedat back focal plane 4100. Accordingly, when optical switch 330 iscontrolled to select light interface 461 and provide the sample light tolight interface 461, then positive lens 370 outputs sample light 345 asa light beam (e.g., a substantially collimated light beam) toward eye10. In that case, the collimated beam may be focused by the opticalpower of eye 10 onto focus position 5001 in first region 5101 on theretina 16 of eye 10. In operation, while optical switch 330 iscontrolled to select light interface 461, scanning mirrors 660 may becontrolled (e.g., by a control signal from processor(s) 160) to scan thesample light in two dimensions (e.g., an x direction and an orthogonal ydirection) to obtain measurements at a number of focal points in region5101. In some embodiments, scanning mirrors 660 may be controlled tomake at least four measurements in region of interest 5104. In someembodiments, scanning mirrors 660 may be controlled to make up to 100measurements in region of interest 5101. In some embodiments, anadditional number of light interfaces may be included in the system toadapt the focus and optical delay of the system to cover the completerange of strongly myopic, myopic, near emmetropic, hyperopic andstrongly hyperopic eyes.

On the other hand, when optical switch 330 is controlled to select lightinterface 464 and provide the sample light to light interface 464, thenpositive lens 370 may produce sample light 345 as a converging lightbeam focused on cornea 12 in region 5104 of eye 10.

Similarly, when optical switch 330 is controlled to select lightinterfaces 462 and 463, respectively, then positive lens 370 may producesample light 345 as a converging light beam focused on the posterior andanterior surfaces, respectively, of lens 14 of eye 10 in regions 5102and 5103, respectively.

Beneficially, optical switch 330 has a relatively rapid switching time.For example, when optical switch 330 is a MEMS device, then theswitching time may be on the order of a few milliseconds. When opticalswitch 330 is based on an electro-optic switch, then the switching timemay be even faster. Through the use or rapid optical switchingtechnologies, in some embodiments OCT measurements may be made for allregions of interest of eye 10 in less than 80 msec, which may preventeye motion during the measurement interval from diminishing or degradingthe quality of the OCT measurements.

When optical switch 330 is controlled to select light interface 461 andprovide the sample light to light interface 461, then the sample lightis scattered and/or reflected by retina 16 in region 5101 of eye 10.This scattered and/or reflected light, referred to here as “returnlight,” passes in the backwards direction back through positive lens 370and impinges on light interface 461, through which it is coupled back tooptical switch 330 via optical fiber 441. The return light then passesback through optical switch 330 to port “C” of optical coupler 320.Optical coupler 320 passes the return light via return path 302 to port“B” from which it is provided to input “X” of light detector 350.

Light detector 350 detects one or more interference signal between thereturn light received at port “X” and the reference light received atport “Y.” Data representing the detected interference signal may beprovided from light detector 350 to processor(s) 160 for measuring oneor more characteristics of region 5101 of eye 10, for example includingretina 16 of eye 10.

Meanwhile, when optical switch 330 is controlled to select lightinterface 464 and provide the sample light to light interface 464, thenthe sample light is scattered and/or reflected by cornea 12 in region5104 of eye 10 and is returned in the backwards direction as returnlight to positive lens 370. The return light passes back throughpositive lens 370 and impinges on light interface 464, through which itis coupled back to optical switch 330 via optical fiber 444. The returnlight then passes back through optical switch 330 to port “C” of opticalcoupler 320. Optical coupler 320 passes the return light to port “B”from which it is provided via return path 303 to input “X” of lightdetector 350, and the resulting interference signal(s) with thereference light are detected.

Similarly, when optical switch 330 is controlled to select lightinterfaces 462 and 463, respectively, then the sample light is scatteredand/or reflected by the posterior and anterior surfaces, respectively,of lens 14 in regions 5102 and 5103, respectively, of eye 10, andreturned back to positive lens 370. The return light passes back throughoptical fibers 442 and 443, respectively, to optical switch 330, port“C” of optical coupler 320, and input “X” of light detector 350 asdiscussed above.

Beneficially, the lengths of optical fibers 441, 442, 443 and 444 areall different from each other so that the delays through the sample pathfor each of the corresponding regions 5101, 5102, 5103 and 5104 arematched to the delay through reference path 304. As explained above, thedelays can be obtained, for example, by loops of fiber 451, 452 and 454.Thus, beneficially, the same optical switch 330 which is used to selecta different light interface for each region of the eye also selects acorresponding delay to be added to match the delay in reference opticalpath 304.

When retina 16 is being measured, then the sample light 345 has to passthrough a depth of eye 10 from lens 14 to retina 16 which may havedispersion characteristics similar to water, which sample light 345 doesnot pass through when cornea 12 is being measured, yielding differentdispersion characteristics. Accordingly, in some embodiments, two ormore (e.g., all) of the optical fibers 441, 442, 443 and 444 may havedifferent dispersions to match the dispersions in the path through eye10 to the particular regions which are being measured via selection ofthose particular optical fibers and their corresponding lightinterfaces. The condition of matching the dispersion and/or the opticaldelay increases the strength of the interference signal.

As described above, MFDL 400 includes a 1:4 optical switch 330 creatingfour channels and four corresponding light interfaces 461, 462, 463 and464 for measuring four corresponding measurement regions 5101, 5102,5103 and 5104 of an object to be measured (e.g., eye 10). Thisconfiguration is convenient when, for example, an OCT subsystem isemployed to measure or characterize four different regions of an objectbeing measured, such as cornea 12, anterior and posterior surfaces oflens 15, and retina 16 of eye 10. However in general it will beunderstood that an OCT subsystem including an MFDL as described abovemay have more or less than four channels with more of less than fourlight interfaces for measuring more or less than four correspondingmeasurement regions of an object to be measured (e.g., eye 10).

As described above, OCT subsystem 300 may measure one or morecharacteristics of eye 10, including measuring a length or distancebetween different features of eye 10 (e.g., between any combination of:cornea 12, anterior and posterior surfaces of lens 14, and retina 16)based on interference signals detected by light detector 350 whendifferent ones of the light interfaces 461, 462, 463 and 464 areselected, for example by processor(s) 160.

FIG. 6 is a functional block diagram of another embodiment of an opticalcoherence tomography (OCT) subsystem 600 that may be included in anoptical measurement system, such as optical measurement system 100 oroptical measurement system 200. OCT subsystem 600 may be one exampleembodiment of OCT subsystem 300 illustrated in FIG. 3.

OCT subsystem 600 includes a light source 610, a beam splitter 620, amulti-focal delay line (MFDL) 625, and a light detector 650. Lightsource 610, beam splitter 620, and multi-focal delay line (MFDL) 625 mayhave the same configurations, respectively, as light source 310, beamsplitter 320, and multi-focal delay line (MFDL) 325 described above withrespect to FIG. 3. MFDL 400 illustrated in FIGS. 4A and 4B may be oneembodiment of MFDL 625 of FIG. 6.

FIG. 6 shows return optical path 602, sample optical path 603 andreference optical path 604 through which the return light, sample lightand reference light, respectively pass.

OCT subsystem 600 also includes polarization paddles 606 for adjustingthe light polarization of the reference light in reference optical path604, and a variable optical attenuator (VOA) 615 for adjusting theamplitude of light 601 output by light source 610.

FIG. 6 also explicitly shows scanning mirrors 660 and an air gap 654serving as a delay (e.g., an adjustable or variable delay) in referenceoptical path 604.

FIG. 6 also illustrates in more detail an example embodiment of lightdetector 650, which may be one embodiment of light detector 350 in FIG.3. Light detector 650 includes a beam splitter 652 and a pair ofdetector elements 653 (e.g., photodiodes). Beneficially, beam splitter652 is a 50/50 beam splitter.

In operation, beam splitter 652 combines the return light received atinput “X” with the reference light at input “Y” to create theinterference signal, which is distributed equally to both output legsbeam splitter 652, which are in turn connected to the pair of detectorelements 653. The 50/50 beam splitter 652 has the property that althoughboth output legs contain the same interference signal, the interferencesignals are 180 degrees out of phase with respect to each other. Theseinterference signals create photo currents in detector elements 653,which are configured as a “balanced photodetector.” That is, detectorelements 653 are stacked on each other with the current output formed bythe difference in photo currents in the two detector elements 652. Thisdifference may generally be picked off between the detector elements653. Thus, the pair of detector elements 653 arranged this way removesthe common mode intensity (background noise) and isolates theinterference fringes. As a result, the interference signal is capturedwith comparatively little background noise.

FIG. 7 is a functional block diagram of yet another embodiment of anoptical coherence tomography (OCT) subsystem 700 that may be included inan optical measurement system such as optical measurement system 100 oroptical measurement system 200. OCT subsystem 700 may be another exampleembodiment of OCT subsystem 300 illustrated in FIG. 3.

OCT subsystem 700 is similar to OCT subsystem 600—especially inoperation—and only differences therebetween will be highlighted. OCTsubsystem 700 includes a light source 710, a first beam splitter 721, asecond beam splitter 622, multi-focal delay line (MFDL) 625, and lightdetector 650. Multi-focal delay line (MFDL) 625 and light detector 650have been described above with respect to FIG. 6, and, again, MFDL 400illustrated in FIGS. 4A and 4B may be one embodiment of MFDL 625 of FIG.7.

Light source 710 includes swept source 712 and a probe source 714. Firstbeam splitter 721 combines the light from swept source 712 and a probesource 714 and outputs reference light to reference path 704 and samplelight to second beam splitter 722 through a first VOA 715. Second beamsplitter 722 receives the sample light and couples it to sample opticalpath 703. Second beam splitter 722 also receives return light from eye10 via MFDL 625 and provides the return light to light detector 650 viareturn optical path 702.

OCT subsystem 700 also includes a second VOA 706 in the referenceoptical path 704.

Otherwise, the construction and operation of OCT subsystem 700 is thesame as for OCT subsystem 600, and the details thereof will not berepeated.

FIG. 8 is a functional block diagram of still another embodiment of anoptical coherence tomography (OCT) subsystem 800 that may be included inan optical measurement system, such as optical measurement system 100 oroptical measurement system 200. OCT subsystem 800 differs principallyfrom OCT subsystems 300, 600 and 700 in that OCT subsystem 800 includesa plurality of “interferometer legs” in the return optical path and thesample optical path.

More specifically, OCT subsystem 800 includes N (e.g., N=4) opticalcouplers 820-1 . . . 820-N disposed in optical paths between opticalswitch 330 and positive lens 370. Each of the optical couplers 820-1 . .. 820-N includes: a first port coupled to an output of optical switch330; a second port coupled to a corresponding return light input oflight detector 850; a third port coupled to a corresponding one of aplurality of light interfaces (e.g., light interfaces 461, 462, 463 or464 of FIG. 4); and a fourth port. A plurality of reference opticalpaths 804-1, 804-2, 804-3 and 804-N are each coupled between the fourthport of a corresponding one of the plurality of optical couplers 820-1 .. . 820-N, and a corresponding reference light input of light detector850. In general, OCT subsystem 800 may include additional elements, suchas variable optical attenuators and scanning mirrors—such as scanningmirrors 660 of FIG. 6. For simplicity of illustration, such elements arenot shown in FIG. 8.

Light detector 850 has a plurality of sample light inputs each coupledto a second port of a corresponding one of the optical couplers 820-1 .. . 820-N, and a corresponding plurality of reference light inputs eachcoupled to an output of a corresponding one of the reference opticalpaths 804-1, 804-2, 804-3 and 804-N. In some embodiments, light detectormay include a plurality of beam splitters such as beam splitter 652,each coupled to one of the sample light inputs and a corresponding oneof the reference light inputs. The outputs of all of the beam splittersmay be provided in close proximity to a common pair of detectorelements, such as detector elements 653 of FIG. 6, and detection maythen proceed as described above with respect to FIG. 6.

In operation, it should be understood that due to the operation ofoptical switch 330, only one of the sample light inputs and acorresponding one of the reference light inputs will actively supplysample light and reference light to light detector 850 at any time.

When measuring eye 10 with OCT subsystem 800, different layer in retina16 may have different intensities of scatter back into OCT subsystem 800for different polarizations. So making measurements with differentpolarizations can reveal different details of retinal anatomy anddisease conditions. Accordingly, in some embodiments, OCT subsystem 800may include one or more polarization control elements, such aspolarization paddles, which may individually optimize the polarizationof the return light, and/or the reference light in each referenceoptical paths 804-1, 804-2, 804-3 and 804-N, for different parts of eye10.

FIG. 9 is a functional block diagram of a further embodiment of anoptical coherence tomography (OCT) subsystem 900 that may be included inan optical measurement system, an optical measurement system such asoptical measurement system 100 or optical measurement system 200. OCTsubsystem 900 is similar to OCT subsystem 800 and only differencestherebetween will be highlighted. OCT subsystem 900 includes: a firstoptical combiner 910 having a plurality of inputs each of which iscoupled to the second port of a corresponding one of the plurality ofoptical couplers 820-1 . . . 820-N, and having an output coupled to thefirst light input (“X”) of light detector 650; and a second opticalcombiner 920 having a plurality of inputs each of which is coupled to onoutput of a corresponding one of the plurality of reference opticalpaths 804-1 . . . 804-N, and having an output coupled to the secondlight input (“Y”) of light detector 650. In some embodiments, first andsecond optical combiners 910 and 920 may each comprise a fiber opticfuser. The addition of first and second optical combiners 910 and 920may simplify the design of the light detector compared to light detector850 of OCT subsystem 800.

FIG. 10 is a functional block diagram of still a further embodiment ofan optical coherence tomography (OCT) subsystem 1000 that may beincluded in an optical measurement system, an optical measurement systemsuch as optical measurement system 100 or optical measurement system200. OCT subsystem 1000 is similar to OCT subsystem 900 and onlydifferences therebetween will be highlighted. In place of first andsecond optical combiners 910 and 920, OCT subsystem 1000 includes asecond optical switch 1010 having a plurality of inputs each of which iscoupled to the second port of a corresponding one of the plurality ofoptical couplers 820-1 . . . 820-N, and having an output coupled to thefirst light input of light detector 650; and a third optical switch 1020having a plurality of inputs each of which is coupled to on output of acorresponding one of the plurality of reference optical paths 804-1 . .. 801-N, and having an output coupled to the second light input of lightdetector 650. Second and third optical switches 1010 and 1020 may becontrolled to be switched in conjunction with the switching of opticalswitch 330.

FIG. 11 is a flowchart of an example embodiment of a method 1100 ofmeasuring one or more optical characteristics of an eye.

In an operation 1110, an optical measurement system including an OCTsubsystem produces sample light and reference light.

In an operation 1120, the optical measurement system controls an opticalswitch to direct the sample light to an object being measured (e.g., aneye), via a first selected light interface and a positive lens.

In an operation 1130, the optical measurement instrument detects one ormore first interference signal(s) from the reference light and returnlight returned from the eye in response to the sample light beingprovided via the first light interface. For example, a scanning mirrormay direct the sample light to a plurality of different focal points ina selected first region of the eye while the sample light is provided tothe eye via the selected first light interface and the positive lens,and a first interference signal may be detected for each of the focuspoints in the first region of the eye.

In an operation 1140, the optical measurement system controls theoptical switch to direct the sample light to an object being measured(e.g., an eye), via a next (e.g., second) selected light interface andthe positive lens.

In an operation 1150, the optical measurement instrument detects one ormore next (e.g., second) interference signal(s) from the reference lightand return light returned from the eye in response to the sample lightbeing provided via the second light interface. For example, a scanningmirror may direct the sample light to a plurality of different focalpoints in a selected second region of the eye while the sample light isprovided to the eye via the selected second light interface and thepositive lens, and a second interference signal may be detected for eachof the focus points in the second region of the eye.

In an operation 1160, an optical measurement system determines thedistance between at least two different features of the eye from thedetected interference signals. For example, the optical measurementinstrument may determine: the distance between the cornea and theanterior surface of the lens, determine the distance between theanterior surface of the lens and the posterior surface of the lens(i.e., thickness of the lens), determine the distance between theposterior surface of the lens and the retina, determine the distancebetween the cornea and the retina, etc.

In an operation 1170, it is determined whether more measurements shouldbe made, in which case the process returns to operation 1140. Otherwise,the measurement operation ends.

All patents and patent applications cited herein are hereby incorporatedby reference in their entirety.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. The term “connected” is to beconstrued as partly or wholly contained within, attached to, or joinedtogether, even if there is something intervening. Recitation of rangesof values herein are merely intended to serve as a shorthand method ofreferring individually to each separate value falling within the range,unless otherwise indicated herein, and each separate value isincorporated into the specification as if it were individually recitedherein. All methods described herein can be performed in any suitableorder unless otherwise indicated herein or otherwise clearlycontradicted by context. The use of any and all examples, or exemplarylanguage (e.g., “such as”) provided herein, is intended merely to betterilluminate embodiments of the invention and does not pose a limitationon the scope of the invention unless otherwise claimed. No language inthe specification should be construed as indicating any non-claimedelement as essential to the practice of the invention. As used herein,the terms first and second are used to describe structures and methodswithout limitation as to the order of the structures and methods whichcan be in any order, as will be apparent to a person of ordinary skillin the art based on the teachings provided herein.

While certain illustrated embodiments of this disclosure have been shownand described in an exemplary form with a certain degree ofparticularity, those skilled in the art will understand that theembodiments are provided by way of example only, and that variousvariations can be made without departing from the spirit or scope of theinvention. Thus, it is intended that this disclosure cover allmodifications, alternative constructions, changes, substitutions,variations, as well as the combinations and arrangements of parts,structures, and steps that come within the spirit and scope of theinvention as generally expressed by the following claims and theirequivalents.

We claim:
 1. An optical coherence tomography system, comprising: a lightsource configured to emit light; a first optical system configured toreceive the light from the light source and to produce therefromreference light and sample light; a reference optical path configured toreceive the reference light from the first optical element; amulti-focal delay line, comprising: an optical switch configured toreceive the sample light from the first optical system and toselectively couple the sample light to a selected light interface amonga plurality of light interfaces, a positive lens system, wherein thelight interfaces are all separated and spaced apart from the positivelens system and located at different distances than each other from aneffective focal plane of the positive lens, wherein the positive lenssystem is configured to receive the sample light from the selected lightinterface, to provide the sample light to an eye, to receive returnlight from the eye, and to provide the return light to the selectedlight interface, wherein the optical switch is further configured toprovide the return light to the first optical system, and the opticalswitch has a plurality of output ports, and a plurality of opticalfibers each having a first end coupled to one of the plurality of outputports, and wherein each of the light interfaces comprises a second endof a corresponding one of the optical fibers; a light detectorconfigured to receive the reference light from the reference opticalpath, and to receive the return light from the first optical system, andin response thereto to detect at least one interference signal; and oneor more processors configured to control the optical switch toselectively couple the sample light to each of the plurality of lightinterfaces, one at a time, and further configured to measure at leastone characteristic of the eye from the detected interference signalswhen the sample light is selectively coupled to the plurality of lightinterfaces.
 2. The system of claim 1, wherein the optical switch has aplurality of output ports, and wherein the multi-focal delay lineincludes a plurality of optical waveguides each connected to one of theoutput ports, the plurality of optical waveguides providing theplurality of light interfaces.
 3. The system of claim 2, wherein each ofthe light interfaces comprises a second end of a corresponding one ofthe optical waveguides.
 4. The system of claim 3, further comprising anintegrated optical circuit including the optical switch, an adjustableoptical delay, and the optical waveguides.
 5. The system of claim 1,wherein each of the optical fibers has a different length.
 6. The systemof claim 1, wherein the one or more processors are further configured todetermine at least one distance between two different areas of the eyefrom the detected interference signals when the sample light isselectively coupled to the light interfaces.
 7. The system of claim 6,where the distances include at least one of: a distance between areference plane and the anterior surface of a cornea, a distance betweena surface of a cornea and a surface of a lens, a distance between asurface of the lens and a retina; and a distance between a surface ofthe cornea and the retina.
 8. The system of claim 1, wherein the opticalsystem includes at least one scanning device configured to scan thesample light on the eye in at least one direction.
 9. The system ofclaim 1, wherein at least one of the light interfaces is distanced fromthe positive lens so that the sample light provided from the opticalsystem to the eye is substantially focused on the retina.
 10. The systemof claim 9, wherein at least another one of the light interfaces isdistanced from the positive lens so that the sample light provided fromthe optical system to the eye is substantially focused on a cornea ofthe eye.
 11. The system of claim 9, wherein at least another one of thelight interfaces is distanced from the positive lens so that the samplelight provided from the optical system to the eye is substantiallyfocused on a lens of the eye.
 12. The system of claim 1, wherein thelight produced by the light source has a coherence length, and whereinthe light interfaces are arranged with respect to the focal plane of thepositive lens system such that the return light from the eye for a firstone of the light interfaces principally comes from a first depth in theeye and the return light from the eye for a second one of the lightinterfaces principally comes from a second depth in the eye differentfrom the first depth, and wherein a distance between the first depth andthe second depth is greater than the coherence length.
 13. The system ofclaim 12, wherein the system is further configured to automaticallychange a delay provided by the multi-focal delay line to match each ofthe first and second depths when the light is output from the first oneof the light interfaces and the second one of the light interfaces,respectively.
 14. The system of claim 1, wherein the light interfacesare all disposed within three degrees of an optical axis of the positivelens.
 15. The system of claim 1, wherein the first optical systemincludes a beam splitter configured to receive the light from the lightsource and to produce therefrom the reference light and the samplelight.
 16. The system of claim 1, wherein the first optical systemincludes a fiber optical coupler configured to receive the light fromthe light source and to produce therefrom the reference light and thesample light.
 17. An optical coherence tomography method, comprising:producing sample light and reference light from a common light source;one or more processors controlling an optical switch to direct thesample light to an eye via a first selected light interface and apositive lens, wherein the optical switch has a plurality of outputports, a plurality of optical fibers each having a first end coupled toone of the plurality of output ports, and wherein each of the lightinterfaces comprises a second end of a corresponding one of the opticalfibers; a light detector detecting at least one first interferencesignal from the reference light and return light returned from the eyein response to the sample light being directed to the eye via the firstselected light interface; the one or more processors controlling theoptical switch to direct the sample light to the eye via a secondselected light interface and the positive lens, wherein the secondselected light interface is disposed at a different distance from afocal plane of the positive lens than the first selected lightinterface; the light detector detecting at least one second interferencesignal from the reference light and return light returned from the eyein response to the sample light being directed to the eye via the secondselected light interface; and obtaining at least one distance between atleast two different features of the eye from the detected first andsecond interference signals.
 18. The method of claim 17, wherein thefirst selected light interface is distanced from the positive lens sothat the sample light provided to the eye is substantially collimated.19. The method of claim 18, wherein the second selected light interfaceis distanced from the positive lens so that the sample light is focusedon a cornea of the eye.
 20. The method of claim 19, further comprisingobtaining a distance between the cornea and a retina of the eye from thedetected first and second interference signals.
 21. The method of claim17, further comprising scanning the sample light in at least onedirection so as to create a plurality of first interference signals fromthe reference light and return light returned from the eye in responseto the sample light being directed to the eye via the first selectedlight interface and to create a plurality of second interference signalsfrom the reference light and return light returned from the eye inresponse to the sample light being directed to the eye via the secondselected light interface.
 22. An optical coherence tomography system,comprising: a light source; a multi-focal delay line, comprising: apositive lens having a focal plane, and a processor-controlled opticalswitch configured to receive a light from the light source and toselectively direct sample light to the positive lens via a selected oneof a plurality of light interfaces each located a different distancefrom the focal plane of the positive lens, wherein the positive lens isfurther configured to direct the sample light to an object to bemeasured, wherein the optical switch has a plurality of output ports,and a plurality of optical fibers each having a first end coupled to oneof the plurality of output ports, and wherein each of the lightinterfaces comprises a second end of a corresponding one of the opticalfibers; and a light detector configured to receive return light returnedfrom the object to be measured in response to the sample light beingdirected to the object to be measured via the positive lens, and toreceive a reference light produced from the light from the light source,and in response thereto to detect at least one interference signal, andmeasure at least one feature of the object.
 23. The system of claim 22,wherein the processor is configured to: control the optical switch todirect the sample light to the positive lens via a first one of theplurality of light interfaces to create at least one first interferencesignal from the reference light and return light returned from theobject to be measured in response to the sample light being directed tothe object to be measured via the first light interface; control theoptical switch to direct the sample light to the positive lens via asecond one of the plurality of light interfaces to create at least onesecond interference signal from the reference light and return lightreturned from the object to be measured in response to the sample lightbeing directed to the object to be measured via the second lightinterface; and determine at least one distance between at least twodifferent features of the object to be measured from the first andsecond interference signals.
 24. The system of claim 22, wherein themulti-focal delay line further comprises: a plurality of opticalcouplers, each optical coupler including: a first port coupled to anoutput of the optical switch, a second port coupled to a correspondingreturn light input of the light detector, a third port coupled to acorresponding one of the plurality of light interfaces, and a fourthport; and a plurality of reference optical paths each coupled betweenthe fourth port of a corresponding one of the plurality of opticalcouplers and a corresponding reference light input of the lightdetector.
 25. The system of claim 22, wherein the multi-focal delay linefurther comprises: a plurality of optical couplers, each optical couplerincluding: a first port coupled to an output of the optical switch, asecond port coupled to a first light input of the light detector, athird port coupled to a corresponding one of the plurality of lightinterfaces, and a fourth port; and a plurality of reference opticalpaths each coupled between the fourth port of a corresponding one of theplurality of optical couplers and a second light input of the lightdetector.
 26. The system of claim 25, further comprising: a firstoptical combiner having a plurality of inputs each of which is coupledto the second port of a corresponding one of the plurality of opticalcouplers, and having an output coupled to the first light input of thelight detector; and a second optical combiner having a plurality ofinputs each of which is coupled to on output of a corresponding one ofthe plurality of reference optical paths, and having an output coupledto the second light input of the light detector.
 27. The system of claim25, further comprising: a second optical switch having a plurality ofinputs each of which is coupled to the second port of a correspondingone of the plurality of optical couplers, and having an output coupledto the first light input of the light detector; and a third opticalswitch having a plurality of inputs each of which is coupled to onoutput of a corresponding one of the plurality of reference opticalpaths, and having an output coupled to the second light input of thelight detector.